For the majority of newborns, cod liver oil is required. The main components of cod liver oil are vitamin A and vitamin D. Newborns are relatively deficient in vitamin A and vitamin D. If newborns spend very little time out in the sun and grow very quickly, they are more likely to have vitamin A and D deficiencies. After the child is deficient in vitamin A, it will cause poor development of the retina, night blindness, dry skin and other symptoms. If a newborn is deficient in vitamin D, it will cause a decrease in calcium absorption, which will lead to vitamin D deficiency rickets, and the child will have excessive sweating, pillow baldness, chicken breast and other manifestations. Therefore, newborns need to take cod liver oil, especially premature babies need to supplement cod liver oil, most children can start supplementing cod liver oil in the first two weeks of life.